Local networks often make use of a communication bus, over which a set of nodes communicates. A driver module in a node acting as a master node applies a voltage to the line, the driver module being switched to produce step changes in the voltage applied to the line to transmit signals over the line to receivers in remote nodes acting as slave nodes. The line also selectively transmits signals from the remote nodes back to a central processing unit. It will be appreciated that certain nodes may be capable of acting both as a master and as a slave node.
Such a bus is used in automotive vehicles, for example. Historically, in automotive applications, functions such as door locks, seat positions, electric mirrors, and window operations have been controlled directly by electrical direct current delivered by wires and mechanical power switches. Such functions may today be controlled by ECUs (Electronic Control Units) together with sensors and actuators in a multiplexed Controller Area Network (CAN). The Controller Area Network (CAN) standard (ISO 11898) allows data to be transmitted by switching a voltage, at a frequency of 250 kbauds to 1 Mbaud for example, to the multiplexed receiver modules over the twisted pair cable. The receiver modules may be actuators that perform a function in response to the signal received, for example by generating mechanical power required or, in the case of sensors, by responding to activation by making measurements and sending the results back to the ECU over the bus.
The CAN bus was designed to be used as a vehicle serial data bus, and satisfies the demands of real-time processing and reliable operation in a vehicle's environment, is cost-effective, and provides a reasonable data bandwidth. However, connecting with the main body network directly via a CAN bus system can be expensive because of increased costs per node and because high overall network traffic can make management extremely difficult. To help reduce costs, the logical extension is to structure the network hierarchically. Among other features, this leads to multicast reception, multi-master operation and message filtering.
A variant on the CAN standard is the LIN (Local Interconnect Network) sub-bus standard (see ISO 7498), which is an extension to the CAN bus, at lower speed and on a single wire bus, to provide connection to local network clusters. A LIN sub-bus system uses a single-wire implementation (enhanced ISO9141), which can significantly reduce manufacturing and component costs. Component costs are further reduced by self-synchronization, without crystal or ceramics resonator, in the slave node. The system is based on common Universal asynchronous receiver and transmitter serial communications interface (UART/SCI) hardware that is shared by most micro-controllers, for a more flexible, lower-cost silicon implementation.
Another related standard is the proposed FlexRay standard. FlexRay is a network communication system targeted specifically at the next generation of automotive applications or ‘by-wire’ applications.
It is important for the current consumption of the nodes of the system to be very low, especially where such systems are powered by a battery or accumulator as in automotive applications. Accordingly, the nodes of the system have standby modes of operation, in which current consumption is reduced when activation of the node is not necessary.
In the case of automotive vehicles, especially cars, the current consumption when the engine is not running is starting to become a very serious problem. The reason is the increase in the number of nodes and other modules and functions that have to be active even while the engine is stopped. The main problem is when the car is parked locked for long periods. By way of example, typical current consumption requirements in the car industry today in parked/locked mode for modules connected directly to the battery are:                100 uA at 12V per module        20 mA at 12V for the whole car        parked for 40 days at −40 degrees C. with enough current left in the battery to start the engine.These requirements are very hard to meet with the complex local networks that are being used more and more in cars, since the master nodes repeatedly wake the slave nodes, for supervision functions, for example.        
Each time a node wakes up in response to a signal applied to the bus, it consumes more current than in the standby mode. Accordingly, it is desirable to include in all relevant nodes a wake-up trigger that is sensitive to an identifier (‘ID’) field of a signal transmitted by a node acting as a master node and selectively wakes up the receiver node only if the received signal contains that ID.
It would be desirable for the network to be capable of handling more than one ID identifying different master nodes as source. This would improve the functionality of the system: in particular, the network could contain more than one master node that could wake slave nodes in standby mode (‘multi-master’), which would otherwise not be possible since it is not acceptable for two or more master nodes to send signals with the same ID. Also, this would enable different groups of slave nodes to wake in response to different master nodes in the same network (‘multicast’). This makes it desirable for the slave nodes to be capable of storing a settable ID corresponding to a selected one of the different IDs, or even more than one settable ID so that they can be woken by more than one master node.
It is also important to minimise the complexity and sophistication of the wake-up part of the slave node that detects the ID, since this will tend to increase its cost and especially its current consumption.